Question

Write a balanced equation for each of the following neutralization reactions: (a) Potassium hydroxide solution is added to phosphoric acid. (b) Strontium hydroxide solution is added to acetic acid.

Short answer

(a) 3KOH + H₃PO₄ → K₃PO₄ + 3H₂O. (b) Sr(OH)₂ + 2CH₃COOH → Sr(CH₃COO)₂ + 2H₂O.

Step-by-step solution

Identify Reactants and Products for Reaction (a)

The reactants for reaction (a) are potassium hydroxide (KOH) and phosphoric acid (H₃PO₄). The products will be water (H₂O) and the salt, which is formed by the cation from KOH and the anion from H₃PO₄, potassium phosphate (K₃PO₄).

Write the Unbalanced Equation for Reaction (a)

Write the chemical equation with reactants on the left and products on the right:\[\text{KOH} + \text{H}_3\text{PO}_4 \rightarrow \text{K}_3\text{PO}_4 + \text{H}_2\text{O}\]

Balance the Equation for Reaction (a)

Balance the potassium ions first by placing a coefficient of 3 in front of KOH: \[3\text{KOH} + \text{H}_3\text{PO}_4 \rightarrow \text{K}_3\text{PO}_4 + \text{H}_2\text{O}\]Balance the water by adjusting the coefficient of H₂O to 3:\[3\text{KOH} + \text{H}_3\text{PO}_4 \rightarrow \text{K}_3\text{PO}_4 + 3\text{H}_2\text{O}\]

Identify Reactants and Products for Reaction (b)

The reactants for reaction (b) are strontium hydroxide (Sr(OH)₂) and acetic acid (CH₃COOH). The products will be water (H₂O) and the salt, strontium acetate, formed by the cation from Sr(OH)₂ and the anion from CH₃COOH (Sr(CH₃COO)₂).

Write the Unbalanced Equation for Reaction (b)

Write the chemical equation:\[\text{Sr(OH)}_2 + \text{CH}_3\text{COOH} \rightarrow \text{Sr(CH}_3\text{COO)}_2 + \text{H}_2\text{O}\]

Balance the Equation for Reaction (b)

Balance the acetate ions first by placing a coefficient of 2 in front of CH₃COOH: \[\text{Sr(OH)}_2 + 2\text{CH}_3\text{COOH} \rightarrow \text{Sr(CH}_3\text{COO)}_2 + \text{H}_2\text{O}\]Balance the water by adjusting the coefficient of H₂O to 2:\[\text{Sr(OH)}_2 + 2\text{CH}_3\text{COOH} \rightarrow \text{Sr(CH}_3\text{COO)}_2 + 2\text{H}_2\text{O}\]

Key concepts

Balanced Chemical Equations

A balanced chemical equation is an expression in which the number of atoms for each element in the reaction and the total charge are the same for both the reactants and products. This means that the law of conservation of mass is followed, indicating that the mass is neither created nor destroyed. When writing a chemical equation, it is important to include all reacting substances on the left side and all produced substances on the right side.

To balance a chemical equation, one adjusts the coefficients (the numbers before compounds or elements) to ensure the same number of each type of atom on both sides of the equation.

For example, in the neutralization reaction between potassium hydroxide and phosphoric acid:

• Original unbalanced: \[ ext{KOH} + ext{H}_3 ext{PO}_4 ightarrow ext{K}_3 ext{PO}_4 + ext{H}_2 ext{O} \]
• Balanced: \[ 3 ext{KOH} + ext{H}_3 ext{PO}_4 ightarrow ext{K}_3 ext{PO}_4 + 3 ext{H}_2 ext{O} \]

Balancing involves ensuring that three potassium atoms and three phosphorous atoms are on both sides of the equation.

Use coefficients wisely to balance complex molecules, and remember to balance polyatomic ions as single units whenever possible.

Acid-Base Reactions

Acid-base reactions are a type of chemical reaction that occurs between an acid and a base. In simple terms, during such reactions, an acid donates a proton (H⁺) to a base. These reactions often produce water and a salt, which is why they are commonly referred to as neutralization reactions.

In reaction \( (a) \), potassium hydroxide, a base, reacts with phosphoric acid, an acid. This creates potassium phosphate, a type of salt, and water:

• General form: \[ ext{Base} + ext{Acid} ightarrow ext{Salt} + ext{Water} \]
• Example: \[ 3 ext{KOH} + ext{H}_3 ext{PO}_4 ightarrow ext{K}_3 ext{PO}_4 + 3 ext{H}_2 ext{O} \]

This pattern holds true in reaction \( (b) \) as well, when strontium hydroxide and acetic acid react to form strontium acetate and water. The exchange of ions forms a neutral set of products. Neutralization not only helps in forming salts but also plays a critical role in various applications, like adjusting the pH of solutions.

In these reactions, it is crucial to identify the acid/base nature of reactants and predict the formation of products based on the neutralization process.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions. It's a fundamental aspect of chemistry that helps in understanding the quantitative relationships in a balanced chemical equation.

The coefficients in a balanced equation represent the ratio in which reactants combine and products form. For example, in the reaction between strontium hydroxide and acetic acid:

• Balanced equation: \[ ext{Sr(OH)}_2 + 2 ext{CH}_3 ext{COOH} ightarrow ext{Sr(CH}_3 ext{COO)}_2 + 2 ext{H}_2 ext{O} \]

Here, the ratio tells us that one molecule of strontium hydroxide reacts with two molecules of acetic acid to produce one molecule of strontium acetate and two molecules of water.

The stoichiometric coefficients are crucial because they allow chemists to calculate how much of each reactant is needed to create a certain amount of product, and vice versa. This is essential not only for laboratory preparations but also for industrial applications such as manufacturing pharmaceuticals and chemicals.

Understanding stoichiometry helps in efficiently using resources, planning chemical reactions, and scaling them from a small to a large scale. It's all about maintaining the balance and proportion as dictated by the chemical equation.